Electronegativity

Question 1

What is “electronegativity?”

Answer 1

• Electronegativity is the power/ ability of an atom to attract the pair of electrons (towards itself) in a covalent bond.

Question 2

What is the “electron distribution” like in a covalent bond between elements that have different electronegativities?

Answer 2

• The electron distribution in a covalent bond between
  elements with different electronegativities will be
  unsymmetrical

Question 3

What occurs to the covalent bond and the molecule when the electron distribution in it in unsymmetrical?

Answer 3

• The covalent bond becomes “polarised.”
• May cause a molecule to have a permanent dipole (two charges: slightly negative/ slightly positive.)

Question 4

What type of molecules will not have permanent dipoles AND for what reason?

Answer 4

• Diatomic molecules will not have permanent dipoles (ie. Cl-Cl/ F-F etc.)
• This is because no atom is more electronegative than the other atom (ie. both atoms have the same electronegativity.)

Question 5

What 4 factors affect electronegativity?

Answer 5

1.) The atoms’ tendency to lose/ gain electrons.
2.) Nuclear charge
3.) Atomic radius
4.) Shielding of nuclear charge by inner electrons/ electron shells.

Question 6

Why does fluorine have a greater electronegativity than hydrogen (even though hydrogen has less electronic shielding?)

Answer 6

• Because fluorine’s tendency is to GAIN electrons whereas, hydrogen’s tendency is to lose electrons.

Question 7

How will increase in nuclear charge of atom affect electronegativity?

Answer 7

• Will increase electronegtaivity because the pair of electrons are more attracted to the positive nucleus of the atom so will move towards this atom.

Question 8

How will increase in atomic radius of atom affect electronegtaivity?

Answer 8

• Decreased electronegativity because weaker force of attraction between positive nucleus (of atom) and negative pair of electrons in the covalent bond.

Question 9

How will increase in electronic shielding affect electronegativity?

Answer 9

• Decrease in electronegativity.
• Less attraction between positive nucleus/ negative pair of electrons in covalent bond.

Question 10

What type of character do some covalent compounds with an atom with high electronegativity exhibit?

Answer 10

• Ionic character (as one atom is essentially “partially gaining” electrons and other atom is “partially losing” electrons.)

() - extra info for clarification.

Question 11

Put these covalent molecules in order of their polarity.
H-O
H-F
H-N

Answer 11

• H all the same.
• Compare electronegativity of O, F, N
• H-N, H-O, H-F

Question 12

How would we draw hydrogen fluoride (showing the permanent dipoles?)

Answer 12

δ+H —– Fδ-
Draw pair of electrons (one cross and one dot) closer to the Fδ- dipole to show how the electrons are unevenly distributed.

Question 13

Give 2 exceptions where a covalent molecule may appear to be polar but it actually isn’t.

Answer 13

(δ-)O = C (δ+) O (δ-) - carbon dioxide.
NF₃

Question 14

Explain why carbon dioxide, although appearing to be polar, is actually non-polar.

Answer 14

(δ-)O = C (δ+) O (δ-)
- Because this molecule (carbon dioxide) is symmetrical, the 2 δ- charges cancel out - this makes the molecule non-polar.

Question 15

Explain why NF₃ although appearing to be polar, is actually non-polar.

Answer 15

• Lone pair on nitrogen will balance out the negative charges on fluorine atoms.
• Electrons are spread out evenly across this molecule.

Question 16

Normally, atoms that have a higher tendency to gain electrons will have a higher electronegativity. Give an exception to this.

Answer 16

• AlCl₃
• Aluminium has high 3+ charge/ is more electronegative than chlorine - so the bond/ pair of electrons on outer shell is polarised.